Signal transducer incorporating a multi-channel photomultiplier tube

ABSTRACT

A multi-channel photomultiplier tube is utilized in a compact optical-to-electrical signal transducer system employed for displaying a film image on the screen of a CRT display device. Optional information derived from scanning the film area with a beam of radiant energy is translated to electrical signals and suitable processed to effect the display imagery. The radiant energy modified by passage through the film image is directed through a condensing lens and a mirror system to convey discrete components of the scanning energy to separate cathode areas of the multi-channel tube, the longitudinal axis of which is substantially in a common plane with the optical axis of the transducer. Utilization of the multi-channel tube promotes compact packaging and provides improved quality of the output of the system.

United States Patent [191 Murphy et al'.

GTE Sylvania Incorporated, Seneca Falls,

Filed: July 10, 1972 Appl. No.: 270,217

[73] Assignee:

US. Cl 178/5.4 E Int. Cl. H0411 9/04 Field of Search. l78/5.4 ES, 5.4 E, 7.2 5.4 ST,

l78/5.4 TC; 313/95 [56] References Cited UNITED STATES PATENTS 6/1971 Jordan l78/5.4E 6/1972 Fisher et al.

DEFLECTION --AND CONTROL CIRCUITRY 5/1962 Parker l78/5.4 ES 7 11 3,787,610 1451 Jan.22, 1974 3,196,205 7/1965 Bedford.. l73/5.4 TC

frederick H. Rin r 1, Cyril A. Krenzer [5 7] ABSTRACT A multi-channel photomultiplier tube is utilized in a compact optical-to-electrical signal transducer system employed for displaying a film image on the screen of a CRT display device. Optional information derived from scanning the film area with a beam of radiant en ergy is translated to electrical signals and suitable processed to effect the display imagery. The radiant energy modified by passage through the film image is directed through a condensing lens and a mirror system to convey discrete components of the scanning energy to separate cathode areas of the multi-channel tube, the longitudinal axis of which is substantially in a common plane with the optical axis of the transducer. Utilization of the multi-channel tube promotes compact packaging and provides improved quality of the output of the system. I

10 Claims, 4 Drawing Figures 75 TUBE CIRCUITRY 1 I- AND SIGNAL 7 PROCESSING PATENTEU JAN 2 P1974 SHEET l [1F 2 PATENTEI] JAN 2 21974 sum 2 or 2 SIGNAL TRANSDUCER INCORPORATING A MULT-I-CI'IANNEL PHOTOMULTIPLIER TUBE CROSS-REFERENCE TO RELATED APPLICATION BACKGROUND OF THE INVENTION This invention relates to an optical-to-electrical signal transducer system utilized for displaying film imag ery on the screen of a cathode ray tube display device and more particularly to a compact signal or transducer system discretely incorporating a single multi-channel photomultiplier tube. Y I

A need exists among the television viewing public, as well as in specialized commercial, industrial and educational endeavors, to utilize television receivers and related types of cathode ray tube display devices for presenting predetermined program displays of slide transparencies, film strips, movies, etc. It has been found that a television type of display device, such as a receiver or monitor, manifests several significant advantages over an optical projection type of display. Film mediums optically projected in a conventional manner usually require a viewing environment having a very low level of ambient light such as that evidenced in a darkened room. Mostof the cooling means associated with the high intensity lamps, necessarily employed in optical projectors, commonly produce ambient noise of an annoying and distracting level. And, inaddition, optical projectors ordinarily have little or very limited means to compensate for inconsistencies and degradations that may bepresent in the film image quality. In contrast thereto, the foregoing exemplary disadvan tages, generally inherent in optical projection, are adequately overcome in a cathode ray tube type of display presentation.

Advantageous results have beenachieved by employing an image reproduction system utilizinga flying spot scanner tube to provide a beam of movinglight to scan the image area of a film, an optical-to-electrical transducer' for converting the optical information, derived from scanning the film image,'to corresponding electrical signals, and a signal processing means wherefrom the signals are suitably applied to a cathode ray tube displaydevice adapted to reproduce the desired image LII necessitates periodic gain adjustments of the individual tubes in order to attempt to maintain the proper color balance of the system. It has been found that the sensitivity and the spectral response characteristics of a photomultiplier tube are apt to change under both shelf-life storage and normal operational conditions. Such deviations are primarily due to variations in the residual gas pressure and changes in material compositions within the individual tubes. Usually, each tube has its own display on the screen thereof. Such systems, whenadapted to color imaging, conventionally utilize a plurality of photomultiplier tubes, usually one for each channel which are arranged to handle the additive primary signals, i.e., red,-blue and green. The bulkiness of using these tubes, along with the associated optical components essential to the system, necessitates space requirements which are at a premium, since it is desired to contain the system into as small a package as possible. In an effort to compact the triple tube system, additional optics have been incorporated which tend to reduce the efficiencies of the system and limit the degree of compaction. In addition, in the plural tube system employing the separate but related photomultipliers, non-uniform aging between the respective tubes often characteristic aging which is determined, to an appreciable extent, by its previous processing history. Thus, the cooperative usage of a plurality of separate tubes in the same system inherently introduces variables which may, over a period of time, markedly and determinately affect the quality of the overall output of the video system. These aspects in addition to the aforementioned bulkiness of the unit are shortcomings of the three tube system.

OBJECTS AND SUMMARY OF THE INVENTION It is an object of the invention to reduce the aforementioned disadvantages by providing an improved optical-to-electrical. signal transducer system.

Further objects of this invention are to provide an optical-to-electrical signal transducer system that prov vides compact packaging, improved quality output, and a minimum of adjustments;

These and other objects and advantages are' achieved in one aspect of the invention by the provision of an optical-to-electrical signal transducer system wherein a multi-channel photomultiplier tube is utilized. A moving beam of radiant energy is focused on. a film image by an objective lens positioned between the source of the scanning energy and the film plane. The modified radiant energy therefrom is conveyed by a condensing lens to a system of beamsplitters and thence to the separate cathode areas of a multi-channel photomultiplier tube. The system provides both compact packaging and improved quality output for the system.

BRIEF DESCRIPTION OF .THE DRAWINGS DESCRIPTION OF THE 'PREFERRED EMBODIMENT For a better understanding of the present invention, together with other and further objects, advantages, and capabilities thereof, reference is made to the following specification and appended claims in connection with the aforedescribed drawings. a

For purposes of simplicity, the various lens designations, denoted in the several schematic figures, while broadly shown as single lenses, are intended to include a variety of lens configurations and multiple lens combinations as are necessary to fulfill the intended functions within the described optical systems. Similarly, the term lens as used in thespecification and appended claims is also intended to broadly encompass a variety of lens configurations and combinations.

in referring to FIG. 1, there is shown an optical-toelectrical signal transducer system 11 utilized in effecting the display of film imagery on the screen of a cathode ray tube display device. Included in the system is a radiant energy scanning means 13 such as a flying spot scanner cathode ray tube having a faceplate 15 with a cathodoluminescent screen 17 disposed on the interior surface thereof. The phosphors in this electron responsive screen are capable. of emitting a substantially broadband of visible spectral emission within the range of substantially 400 to 700 nanometers. To control movement of the screen-impinging electron beam 19 within the tube, suitable deflection and control signals are appropriately applied to the tube environment from the deflection and control circuitry 21. impingement of the moving electron beam 19 on the cathodoluminescent screen 17 excites immediate areas of the phosphor therein and produces a moving beam of luminescent radiant energy or light 23 which projects outward from the faceplate portion. Usually only a small area of the tube faceplate 15 is utilized for demarcating the raster of the moving beam of light 19, such being denoted as a scanning pattern dimensionally defined as a.

An objective or converging-type lens 25 is located in optical alignment with substantiallythe center of the raster pattern to receive the moving beam of scanning light, and.to focus the luminescent raster pattern b thereof through a masking means 26 onto the plane of the, image area 27 of the film medium 29 which is positioned by appropriate film orientation means 31.

The moving beam of light 23, upon passing through the fiim imagery 27 is modulated or-modified in accordance with the density of the dyes therein. The modified light is thence collected by a' condensing or collecting lens 33 and directed to a signal conversionv section 35 wherein the optical information is converted to electrical signals.

ln greater detail, as shown in FIG. l, the modified light conveyed by the condensing lens 33 is directed to a system of differentially selective reflective surfaces 37 in the form-of first and second beamsplitting dichroic mirrors, 39 and 41 respectively, which are selective filter means known in the art for splitting or dividing incident light into red, blueand green color components. These are arranged tandemwise in optical alignment and in spaced relationship, in conjunction with a sequentially oriented broad-band front-surface reflective mirror 43, to selectively direct the separated color components of theimage-modulated light to separate cathode areas of photomultiplier means 45. In this instance, the photomultiplier means is a multi-channel tube 45 having a longitudinal axis 47 and a plurality of separated cathode areas 49, 51, and 53 longitudinally located in an in.-line manner in a plane 57 substantially parallel to the axis of the tube. Each of the separate cathode areas has an associated'window area defined respectively as 48, 50, and 52 by opaque masking means 54'disposed relative to the exterior of the envelope 59. As illustrated, the longitudinal axis of the tube 47 and .the optical axis of alignment 55 of the transducer system are in a substantially common plane. Similarly, the longitudinal axis of the tube is substantially parallel with the optical axis of the condensing lens 33 which is coincident with the optical axis of alignment As schematically illustrated, the three-channel photomultiplier tube is, for example, of a conventional circular photomultiplier structure. For a description of a multi-channel photomultiplier tube, reference is directed to U.S. Pat. No. 3,668,388 by M. B. Fisher et al and assigned to the assignee of the present invention. Briefly, the internal construction of such a tube is enclosed within a glass envelope 59 which, being free of optical distortions, exhibits high and broad-band light transmission characteristics to facilitate efficient passage of incident light therethrough. The internal structure encompassed therein, of which a minimum of elements are symbolically detailed, comprises a common grid 61; a common photocathode 63 having the three separate active cathode areas 49, 51' and 53 thereon; a plurality of common related dynode members of which only two are shown and plurally designated as 65, each of the dynode members having separate channel areas thereon whence secondary electrons are-readily emitted; and separate anode elements 69, 71 and 73 for each of the three channels. The common grid member 61, the common photocathode member 63, each of the common dynode members 65, and each of the distinct anode elements have separate conductive leads extending externally from the envelope 59. These separate leads make appropriate'electrical connections with the tube and signal processing circuitry 75 which, in turn, translates the input signals to appropriate output sig-' nals of the .type usable. in the image display device 77 to effect a reproduction display of thefilm image 27.

'These discrete output signals are conveyed to the CRT display device by wire or wireless means as indicated by the Z-Z connection.

The beamsplitting mirror system 37 is oriented in a manner that the first dichoric mirror 39 is positioned at a substantially 45 angle to the optical axis of the incoming diffused light. This first mirror exhibits an optical filter characteristic. which selectively reflects a defined range of spectral emission'defining one color component of the incident diffused or unfocused light beam, as for example red, directing the same through the envelope window 48 to impinge the end cathode area 49. The remainder of the modified light beam inci dent on the first dichroic mirror 39 passes therethrough andstrikes the second dichroic mirror 41. This mirror manifesting a different filter characteristic, selectively reflects and directs another range of spectral emission of a second color component of the incident unfocused light, as forexample blue, through envelope window 50 to impinge the middle cathode area 5l. The remaining incident light passedby the second dichroic mirror 41, representing a third color emission component of the imagery, as for example green, contacts the front surface reflective mirror 43 and is angularly directed through the window 52 to impinge the third or end cathode area 53.

In the embodiment shown in FIG. 1, the'diffused light I striking the first tube window 48 is of an area larger than the area of light incident upon the third tube window 52 since the path of light from the condensing lens is of a shorter length. The differences of incident light intensity for the respective cathodes are compensated by gain adjustments in the signal processing section 75.

For another embodiment of'the invention, reference is made to FIGS. 2 and 3 wherein the multi-channel photomultiplier tube 45 is positioned in a manner that the paths for the red, blue and green light components are of substantially equal lengths. Thus, the three diffused beams of the separate light components exhibit substantially equal areas of impingement whereof the intensity of the discrete color component striking the respective cathode surface in the multi-channel tube is of the value substantially inherent in the composite light leaving the condensing lens 33. By the arrangement shown, the tube 45 is positioned with the longitudinal axis 47 thereof making an acute angle fiof, for example 45, with the optical axis 55 of the con ensing lens, which is also the optical axis of the alignment of the light incident to the mirror system 37. With the tube so located, the discrete light components or defined ranges of spectral energy reflected by the respective surface of the reflective means 39, 41' and 43 of the mirror system 37 strike the surface of the envelope win-.

dow areas 58, 50 and 52 at an angle. For instance, an exemplary ray of light 101 reflected from dichroic mirror 39 strikes the window area surface of the tube envelope 59 at an angle of incidence i of substantially 45 with reference to the normal 103 to that surface. With a light ray having this angle of incidence relative to a bare glass surface, there is appreciable reflectance as evidenced by the angle of reflection R."This condition represents a considerable loss of light which desirably should be directed through the glass of the window region 48 to impinge the respective cathode area 49 therebeneath. To remedy this deleterious condition and expedite desirable transmission of the light ray 101 through the glass, an antireflective (AR) coating 105 such as magnesium fluoride is applied to the outer surface of the window area of the envelope. Multilayer coatings are also applicable to this utilization. Since the light ray 101 penetrates the AR coating in an oblique manner, the thickness of the coating is less than substantially one-fourth wavelength of the light incident thereon. To further increase the optical efficiency, the AR coatings disposed on the individual respective window areas can each be tailored with respect to the specific range of. spectral energy directed thereto. The light ray 101 in passing from the air atmosphere 109, and traveling obliquely through'the envelope glass material 59, is refracted toward the normal 103; and in emerging from the glass into thevacuum environment 111 of the tube interior is bent away from the normal into a plane nearly parallel with the plane of incidence.

As shown in FIGS. 2 and 3, the angling of the incident light into the multi-channel tube 45 necessitates repositioning or longitudinally shifting of the opaque masking means 54 to assure proper impingement of the incident light on the respective cathode areas.

Still another embodiment of the invention is referenced in FIG. 4, wherein the multi-channel tube 45 is likewise angularly positioned to provide light paths of substantially equal lengths for the red, blue and green color components. This third embodiment is a simplitied and more compact version of the second embodimentdelineated in FIG. 2. The tube is located with its longitudinal axis 47 making an acute angle 1, such as of 45, with the optical axis 55 of the condensing lens 33. To further explicate tube orientation in this embodiment, the angled tube positioning is such that the 6 aforementioned optical axis 55 of the condensing lens 6bTiqu elyintersects the end cathode area at an angle of substantially 45. A simplified mirror system 37 is employed wherein only the two sequentially positioned beamsplitting dichroic mirrors 39 and 41 are utilized to handle two of the spectral energy components, such as red and blue; directing the same to the respective cath- 5 ode areas 49 and 51 within the tube. The third color component, such, as the green, traverses both of the l mirrors and directly enters the tube 45, obliquely impinging the end cathode area 53 at an angle of substanitially 45. N W mm" The embodiment shown in FIG. 4 also desirably employs anti-reflective coating on the exterior surface of the window areas of themulti-channel tube for the ma son already described.

' rims; there is provided an improved optical-toelectrical signal transducer system that, by expeditiously employing a multi-channel photomultiplier, requires a minimum of adjustments, evidences enhanced quality output and lends itself to compact packaging. The multi-channel tube represents distinct improvements not realized when utilizing a plurality of separate photomultiplier tubes. The related operational characteristics of the several channels in a common envelope environment provide marked improvement in the handling of the separate optically induced signals and enhances the quality of the output. The several channels, being within the common envelope of the tube, are exposed to the same processing history and are operated in the same residual atmosphere. Hence, all of the channels exhibit substantially similar aging characteristics, and a related color balance is maintained througout the life of the tube. Additionally, the use of the compact multi-channel tube in the transducer system represents cost and space saving advantages in the video application and facilitates reduction in the complexity of the associated operational circuitry;

While there has been shown and described what are at present considered the preferred embodiments of the invention, it will be obviousto those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.

What is claimed is:

l.'An optical-to-electrical signal transducer system having an optical axis of alignment and wherein optical information derived from the scanning of a fllm image area by a moving beam of radiant energy is translated to electrical signals suitable for processing to effect a display of the film image on the screen of a cathode ray tube display device, said transducer system comprising:

"a'saureebra moviagbam of radiant energy emanatingas a scanning raster pattern; means for orienting said film image in a plane relative to said moving beam of radiant energy; an objective lens positioned between said source of radiant energy and said film plan in a manner to focus said moving beam on the image area thereat', a multi-channel photomultiplier tube having a longitudinal axis and at least first and second separated cathode areas longitudinally located in an in-line manner in a plane substantially parallel to the axis of said tube, each of said separate cathode areas having an associated window area defined by opaque masking means disposed relative to the exi terior of said envelope, each of said window areas being oriented to receive the component of incident radiant energy discretely directed thereto, the axis of said tube and the optical axis of said transducer being in a substantially common plane;

a condensing lens having an optical axis positioned in said optical alignment between said film plane and said multichannel photomultiplier tube to convey 'the modified radiant energy from said film image to said photomultiplier tube; and

a system of differentially selective reflective surfaces in the .form of a plurality of beamsplitting dichroic mirrors substantially arranged tandemwise in the plane of said optical axis of alignment and in spaced relationship and similar orientation to angularly convey discrete components of said modified radiant energy to separate cathodes of said multichannel tube. I

2. An optical-to-electrical signal transducer system according to claim 1 wherein said multi-channel photomultiplier tube is positioned with the longitudinal axis thereof substantially parallel with the optical axis of said condensing lens, and wherein the discrete components of said modified radiant energy impinge the respective cathode areas of said rnulti-channel tube at angles substantially normal thereto.

3. An optical-to-electrical signal transducer system according to claim 1 wherein said multi-channel photomultiplier tube is positioned with the longitudinal axis thereof making an acute angle with the optical axis of said condensing lens to provide for radiant energy paths of substantially equal lengths, each of said individual components of modified radiant energy making oblique angular impingement on a respective cathode area of said tube. v

4. An optical-to-electrical signal transducer system according to claim 3 wherein said multi-channel photomultiplier tube is positioned with the longitudinal axis thereof making an angle of substantially 45 with the optical axis of said condensing lens.

5. An optical-to-electrical signal transducer system according to claim 2 wherein a broad-band frontsurface reflective mirror is positioned tandemwise and in spaced relationship to a last of said dichroic mirrors in said mirror system to reflect a remaining component to a separate discrete cathode area in said photomultiplier tube.

6. An optical-to-electrical signal transducer system according to claim 1 wherein said multi-channel photomultiplier tube is positioned with the longitudinal axis thereof making an acute angle with optical axis of said condensing lens to provide for radiant energy paths of substantially equal lengths, and wherein said optical axis angularly impinges an end cathode area of said multiple section photomultiplier tube.

7. An optical-to-electricalsignal transducer system according to claim 6 wherein said multi-channel photomultiplier tube is positioned with the longitudinal axis thereof making an angle of substantially 45 with the optical axis of said condensing lens, and wherein said optical axis obliquely intersects said end cathode area at an angle of substantially 45.

8. An opticalto-electrical signal transducer system according to claim 3 wherein said multi-channel photomultiplier tube has an anti-reflective coating disposed on the exterior surface of the envelope over the cathode areas. 1 v

9. An optical-to-electric'al signal transducer system according to claim 8 wherein the anti-reflective coating disposed on the exterior surface of said photomultiplier envelope has a thickness of less than substantially onefourth wavelength of the radiant energy incident thereon.

.10. An optical-to-electrical signal transducer system according to claim 3 wherein the window areas defined by said opaque masking means, associated with said multi-channel tube, are positioned in a longitudinal offset manner from the related cathode areas to assure substantially equal areas of impingement of the respective diffused components of incident light on the angularly oriented cathode areas. 

1. An optical-to-electrical signal transducer system having an optical axis of alignment and wherein optical information derived from the scanning of a film image area by a moving beam of radiant energy is translated to electrical signals suitable for processing to effect a display of the film image on the screen of a cathode ray tube display device, said transducer system comprising: a source of a moving beam of radiant energy emanating as a scanning raster pattern; means for orienting said film image in a plane relative to said moving beam of radiant energy; an objective lens positioned between said source of radiant energy and said film plan in a manner to focus said moving beam on the image area thereat; a multi-channel photomultiplier tube having a longitudinal axis and at least first and second separated cathode areas longitudinally located in an in-line manner in a plane substantially parallel to the axis of said tube, each of said separate cathode areas having an associated window area defined by opaque masking means disposed relative to the exterior of said envelope, each of said window areas being oriented to receive the component of incident radiant energy discretely directed thereto, the axis of said tube and the optical axis of said transducer being in a substantially common plane; a condensing lens having an optical axis positioned in said optical alignment between said film plane and said multichannel photomultiplier tube to convey the modified radiant energy from said film image to said photomultiplier tube; and a system of differentially selective reflective surfaces in the form of a plurality of beamsplitting dichroic mirrors substantially arranged tandemwise in the plane of said optical axis of alignment and in spaced relationship and similar orientation to angularly convey discrete components of said modified radiant energy to separate cathodes of said multichannel tube.
 2. An optical-to-electrical signal transducer system according to claim 1 wherein said multi-channel photo-multiplier tube is positioned with the longitudinal axis thereof substantially parallel with the optical axis of said condensing lens, and wherein the discrete components of said modified radiant energy impinge the respective cathode areas of said multi-channel tube at angles substantially normal thereto.
 3. An optical-to-electrical signal transducer system according to claim 1 wherein said multi-channel photo-multiplier tube is positioned with the longitudinal axis thereof making an acute angle with the optical axis of said condensing lens to provide for radiant energy paths of substantially equal lengths, each of said individual components of modified radiant energy making oblique angular impingement on a respective cathode area of said tube.
 4. An optical-to-electrical signal transducer system according to claim 3 wherein said multi-channel photomultiplier tube is positioned with the longitudinal axis thereof making an angle of substantially 45* with the optical axis of said condensing lens.
 5. An optical-to-electrical signal transducer system according to claim 2 wherein a broad-band froNt-surface reflective mirror is positioned tandemwise and in spaced relationship to a last of said dichroic mirrors in said mirror system to reflect a remaining component to a separate discrete cathode area in said photomultiplier tube.
 6. An optical-to-electrical signal transducer system according to claim 1 wherein said multi-channel photomultiplier tube is positioned with the longitudinal axis thereof making an acute angle with optical axis of said condensing lens to provide for radiant energy paths of substantially equal lengths, and wherein said optical axis angularly impinges an end cathode area of said multiple section photomultiplier tube.
 7. An optical-to-electrical signal transducer system according to claim 6 wherein said multi-channel photomultiplier tube is positioned with the longitudinal axis thereof making an angle of substantially 45* with the optical axis of said condensing lens, and wherein said optical axis obliquely intersects said end cathode area at an angle of substantially 45*.
 8. An optical-to-electrical signal transducer system according to claim 3 wherein said multi-channel photomultiplier tube has an anti-reflective coating disposed on the exterior surface of the envelope over the cathode areas.
 9. An optical-to-electrical signal transducer system according to claim 8 wherein the anti-reflective coating disposed on the exterior surface of said photomultiplier envelope has a thickness of less than substantially one-fourth wavelength of the radiant energy incident thereon.
 10. An optical-to-electrical signal transducer system according to claim 3 wherein the window areas defined by said opaque masking means, associated with said multi-channel tube, are positioned in a longitudinal off-set manner from the related cathode areas to assure substantially equal areas of impingement of the respective diffused components of incident light on the angularly oriented cathode areas. 